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Abstract:

A method of controlling spectrum use in a first wireless communications
system which is operable to take part in a spectrum assignment process
involving a plurality of wireless communications systems including the
first wireless communications system, in which spectrum assignment
process one of the said wireless communications systems assigns a portion
of spectrum to at least one of the other said wireless communications
systems. The method comprising effecting an instance of the spectrum
assignment process in response to a trigger which is based on network
conditions.

Claims:

1. A method of controlling spectrum use in a first wireless communications
system which is operable to take part in a spectrum assignment process
involving a plurality of wireless communications systems including the
first wireless communications system, in which spectrum assignment
process one of the said wireless communications systems assigns a portion
of spectrum to at least one of the other said wireless communications
systems, the method comprisingeffecting an instance of the spectrum
assignment process in response to a trigger which is based on network
conditions.

2. The method of claim 1 comprising periodically effecting instances of
the spectrum assignment process, in accordance with a time period
determined in dependence on the network conditions.

3. The method of claim 1 comprising determining a traffic delivery success
ratio for the first wireless communications system and effecting the
instance of spectrum assignment process in response to the traffic
delivery success ratio being under a predetermined threshold.

4. The method of claim 1 wherein the spectrum assignment process is a
long-term spectrum assignment process, the method comprising receiving
signalling being indicative of the failure of a short-term spectrum
assignment process, and effecting the instance of the long-term spectrum
assignment process in response to the number of failures of the
short-term assignment process exceeding a predetermined threshold.

5. The method of claim 1 wherein effecting the instance of the spectrum
assignment process comprises obtaining, for each of the wireless
communications systems involved in the process, a preferred spectrum
configuration, and calculating a final spectrum configuration based on
the preferred spectrum configurations.

6. The method of claim 5 wherein obtaining the preferred spectrum
configurations comprises receiving from each of the other said wireless
communications systems signalling to indicate their respective preferred
spectrum configurations, and further comprises obtaining the preferred
spectrum configuration for the first wireless communications system by
calculating an amount of additional/surplus spectrum for the first
wireless communications system and using the amount of additional/surplus
spectrum to determine the size of a chunk of spectrum for allocation to
the first wireless communications system;estimating the sizes of
respective chunks of spectrum for allocation to each of the other
wireless communications systems involved in the spectrum assignment
process; andarranging the chunks of spectrum to form the preferred
spectrum configuration for the first wireless communications system.

7. The method of claim 6 wherein calculating the amount of
additional/surplus spectrum for the first wireless communications system
comprises determining an amount of spectrum which is required by the
first wireless communications system, or which is available for
assignment from the first wireless communications system to one or more
of the other said wireless communications systems, based on parameters
including at least one or more of a traffic delivery success ratio and a
level of interference associated with the first wireless communications
system.

8. The method of claim 7 wherein the determination comprises using a
mapping table to obtain the amount of additional/surplus spectrum from
the said parameters.

10. The method of claim 9 wherein each preferred spectrum configuration
comprises one or more suggested chunks of spectrum for allocation
respectively to one or more of the wireless communications systems
involved in the spectrum assignment process, and wherein the averaging
comprises calculating a final chunk of spectrum for each of the said
wireless communications systems by summing all of the suggested chunks of
spectrum for allocation to that wireless communications system and
dividing by the number of wireless communications systems involved in the
spectrum assignment process.

11. The method of claim 5 performed by the first wireless communications
system, wherein the first wireless communications system is a lead
wireless communications system amongst the wireless communications
systems involved in the spectrum assignment process.

12. The method of claim 11 comprising transferring the status of lead
wireless communications system from the first wireless communications
system to another of the plurality of wireless communications systems in
dependence on a predetermined arrangement.

13. The method of claim 1 wherein effecting the instance of the spectrum
assignment process comprises transmitting to a central spectrum broker
module spectrum-related signalling, and receiving signalling from the
central spectrum broker module to indicate a final spectrum
configuration.

14. The method of claim 3 wherein calculating a traffic delivery success
ratio comprises determining a ratio of the quantity of traffic delivered
to/from the first wireless communications system to the quantity of
traffic which was intended for delivery to/from the first wireless
communications system.

15. The method of claim 1 wherein the spectrum assignment process is a
long-term spectrum assignment process forming part of a larger spectrum
sharing scheme further including at least a short-term spectrum
assignment process.

16. The method of claim 1 wherein the spectrum assignment process involves
at least three wireless communications systems including the first
wireless communications system.

17. The method of claim 5 wherein one or more of the preferred spectrum
configurations of respective wireless communications systems and the
final spectrum configuration comprises a region of dedicated bandwidth
and a region of extra shared bandwidth.

18. The method of claim 1 wherein two or more of the wireless
communications systems involved in the spectrum assignment process
comprise two or more respective groups of one or more network elements,
the groups forming parts of the same overarching network, the method
comprising the said two or more wireless communications systems
independently taking part in the spectrum assignment process.

19. Apparatus for controlling spectrum use in a first wireless
communications system which is operable to take part in a spectrum
assignment process involving a plurality of wireless communications
systems including the first wireless communications system, in which
spectrum assignment process one of the said wireless communications
systems assigns a portion of spectrum to at least one of the other said
wireless communications systems, the apparatus comprisingspectrum
assignment circuitry configured to effect an instance of the spectrum
assignment process in response to a trigger which is based on network
conditions.

20. A computer program which, when run on a computer forming part of a
network element or an external controlling element, causes the computer
to perform a method of controlling spectrum use in a first wireless
communications system which is operable to take part in a spectrum
assignment process involving a plurality of wireless communications
systems including the first wireless communications system, in which
spectrum assignment process one of the said wireless communications
systems assigns a portion of spectrum to at least one of the other said
wireless communications systems, the method comprisingeffecting an
instance of the spectrum assignment process in response to a trigger
which is based on network conditions.

Description:

[0001]This application claims priority to United Kingdom Application No.
0801532.3 filed on Jan. 28, 2008, the disclosure of which is expressly
incorporated herein by reference in its entirety.

[0002]The invention relates to a method of, and apparatus for, controlling
spectrum use in a wireless communications system.

BACKGROUND

[0003]The increasing demand for flexible use of the radio spectrum for
emerging new services and applications is the motivation behind numerous
research activities worldwide. Efficient access to radio spectrum
resources will generate new sources of revenues for worldwide vendors and
wireless network operators. Recent studies worldwide indicate that while
some systems and mobile operators are starving for more efficient
utilization of spectrum resources, most of the radio spectrum resources
remain underutilized or unused most of times. The new design of wireless
radio infrastructure outlines the new attempts to share the spectrum in a
fundamentally novel fashion which would ultimately lead to better
utilization of spectrum. The proposed spectrum management architectures
and the spectrum sharing functionalities developed recently will result
in reducing the time required to tailor a new service to an operator
network. Furthermore, the flexible spectrum access and usage leads to
more capable and faster services with high Quality of Service (QoS)
giving more user satisfaction than conventional networks.

[0004]FIG. 1 shows a proposed architecture in a potential scenario where
different radio access networks (RANs) are engaged in so-called long-term
and short-term spectrum assignment processes. The central diagram of FIG.
1 shows three gateways GW of respective radio access networks RAN1-3
taking part in a LT spectrum negotiation, while the individual base
stations of the three RANs 1-3 take part in ST spectrum negotiations. The
two graphs to the left of FIG. 1 represent the amount of spectrum
allocated respectively to the first base station BS1 of the first radio
access network RAN1 and to the second base station BS2 of the second
radio access network RAN2. As can be seen in each of the graphs, the
low-frequency curve represents the amount of spectrum allocated to the
respective base station as a result of LT spectrum negotiations, while
the high-frequency curve represents the amount of spectrum as a result of
ongoing ST spectrum negotiations. The diagram to the right of FIG. 1
shows the spectrum boundaries set by LT spectrum assignment being
adjusted by ST spectrum assignment, in this case with BS3 of RAN3
borrowing a chunk of spectrum from BS2 of RAN2 in the ST spectrum
assignment process.

[0005]FIG. 2 shows a novel system for spectrum sharing and coexistence.
The possibility of spectrum exchange between two or more RANs has been
proposed and may ultimately lead to a better utilization of spectrum for
wireless mobile networks. In FIG. 2, base stations negotiate over the air
during ST spectrum assignments, and may take part in horizontal sharing
(a type of sharing in which there is no priority among RANs) while
gateways negotiate over an external IP network during LT spectrum
assignments, and may take part in vertical sharing (a type of sharing in
which one RAN has priority over other RANs). The gateways communicate
with a central database, which includes information regarding spectrum
policies and regulations, and may also include historical logs of
spectrum access and assignments.

[0006]The basic idea is to let independent radio access networks (RANs)
use the spectrum of other RANs when it is not needed by those RANs. The
RANs may negotiate using proposed gateways (GWs).

[0007]Four stages for the spectrum negotiations and management have been
proposed:

[0008]Spectrum Co-Existence and Sharing

[0009]In the first stage, RANs (perhaps belong to different operators)
decide on the size of a shared spectrum band which might be available
from one of those RANs beyond their existing dedicated spectrum band. A
typical scenario is shown in FIG. 3, in which a dedicated band licensed
to RAN1-3 is extended by borrowing extra shared bandwidth. The decision
on the precise final boundaries of spectrum is location-dependent and
also depends on the nature of the area, e.g. metropolitan area, local
area and the coordinates (X,Y) of the RANs and is based on the trade-off
between spatial separation and frequency separation. FIG. 4 illustrates a
typical scenario for a cellular configuration, including three adjacent
cells. It can be observed in FIG. 4 that the initial boundaries of
available spectrum are different on a cell-by-cell basis.

[0010]Long Term (LT) Spectrum Assignment

[0011]In the second stage, after making the decision about the boundaries
of spectrum, a negotiation occurs on a couple of minutes' basis through
negotiations between gateways assigned to different RANs (i.e. from the
different operators) to rearrange the available spectrum to maximize the
utilization of spectrum, say between a primary and a secondary system.
The idea is to give the capability to each mobile operator to trade its
unused spectrum in order to maximize revenue and to provide a new extra
source of spectrum when needed to improve the QoS. As depicted in FIG. 5,
the spectrum boundaries and guard bands are changed on a couple of
minutes basis depending on traffic conditions, the assigned and agreed
policy and regulations.

[0012]Short Term (ST) Spectrum Assignment

[0013]In the third stage, after making the decision about the boundaries
of spectrum, a negotiation occurs on a one second or couple of second
basis locally between the base stations as depicted in FIG. 1. A typical
scenario is depicted in FIG. 6 where a base station from a Metropolitan
Area (MA) Deployment has managed to progressively negotiate and get
spectrum from a Wide Area (WA) deployment.

[0014]Channel Allocation/Radio Resource Partitioning

[0015]We assume that, in both the physical layer and the network layer,
the radio specifications can be changed in order to provide an acceptable
level of BER. At the network level, the interference can be minimised by
applying channel allocation/radio resource partitioning (i.e. by suitable
selection of channel frequency). After a decision is reached regarding ST
Spectrum Assignment, a decision is made on a couple of 10 ms basis to
allocate suitable sub-channels to each cell or base station. This is
depicted in FIGS. 7A and 7B. Channel allocation also can be applied at
the base station (BS) level where the BS decides how to allocate the
sub-channels to user equipment (UEs) (perhaps using another smaller
sub-channel arrangement).

[0016]FIG. 8 shows the hierarchy of the four stages of spectrum assignment
based on the employed time granularity. Spectrum Co-existence and Sharing
operates on a timescale of hours or a couple of days. LT Spectrum
Assignment operates on a timescale of a minute or a couple of minutes. ST
Spectrum Assignment operates on a timescale of a second or a couple of
seconds. Channel Allocation/Radio Resource Partitioning operates on a
timescale of 10 ms or a couple of 10 ms.

SUMMARY

[0017]According to a first aspect, there is provided a method of
controlling spectrum use in a first wireless communications system which
is operable to take part in a spectrum assignment process involving a
plurality of wireless communications systems including the first wireless
communications system, in which spectrum assignment process one of the
said wireless communications systems assigns a portion of spectrum to at
least one of the other said wireless communications systems, the method
comprising

[0018]effecting an instance of the spectrum assignment process in response
to a trigger which is based on network conditions.

[0019]The method may be particularly useful in the case of long-term (LT)
spectrum management where potential triggers for the LT spectrum
assignment are produced. The method may improve the spectral efficiency
by exploiting the availability of spectrum on a long-term basis by taking
advantage of the current traffic and radio channel conditions and the
traffic success delivery ratio since the last LT spectrum assignment. The
method may provide a further fine tuning to Spectrum Co-existence and
Sharing. It may make it possible to exploit the availability of spectrum
from one RAN to other RANs, and to improve the QoS, the overall network
coverage and throughput, and the revenue for the borrowing party by
making sure that the radio resource is available when needed in peak
times. Operators may benefit from an extra source of income as the
lending party by making sure that the redundant radio spectrum is not
wasted and employed in an efficient way. The potential for call blockage
may be reduced by providing better and more efficient access to more
radio resources. The method may be applicable to LT Spectrum Assignment
for negotiations with and without priorities.

[0020]The term "wireless communications system" may relate to a wireless
access network, for example a radio access network (RAN), including all
of the elements of the network, for example base stations. Additionally
or alternatively, it may relate to communications apparatus, for example
a network element, e.g. a base station. In another arrangement, it may
relate to an RFID tag reader, to a sink or wireless sensor network base
station, or to a group of such readers forming a network, possibly
including other equipment, e.g. control circuitry. It may also relate to
a WiMAX network.

[0021]The spectrum assignment process may comprise the re-assignment of a
portion of a spectrum band which has been pre-assigned to one of the
first and a second wireless communications system from the one wireless
communications system to the other of the first and second wireless
communications systems. In other words, where a first spectrum band has
been pre-assigned to the first wireless communications system, and a
second spectrum band has been pre-assigned to the second wireless
communications system, the spectrum assignment process may comprise (for
example during negotiations between the first and second wireless
communications systems) re-assigning, from one of the first and second
wireless communications systems to the other of the first and second
wireless communications systems, some or all of the respective first or
second pre-assigned spectrum band. By "pre-assigned" it may be meant that
the wireless communications system to which the spectrum band has been
pre-assigned is licensed for operation within that spectrum band. The act
of assigning a portion of spectrum from one system to another may
comprise the one system giving permission to the other system to use the
assigned portion of spectrum, whereafter the one system ceases to operate
using the assigned portion, while the other system may choose to operate
using the assigned portion if desired. The spectrum assignment process
may relate in particular to a long-term spectrum assignment process
forming part of a larger spectrum sharing scheme further including at
least a short-term spectrum assignment process. The spectrum assignment
process may involve at least three wireless communications systems
including the first wireless communications system. The term "instance"
when used in relation to the spectrum assignment process may refer to a
single assignment of spectrum (potentially including a plurality of
spectrum portions) by means of the spectrum assignment process.

[0022]By "spectrum" there may be meant radio frequencies or any other
range of frequencies of electromagnetic radiation suitable for
communication. For example, the first and second wireless communications
systems may be radio access networks (RANs) operating within the radio
frequency range of the electromagnetic spectrum. Additionally or
alternatively, the wireless communications systems may operate within a
microwave frequency range, for example.

[0023]The terms "portion" or "band" when used in relation to spectrum may
relate to a particular range of frequencies, which may consist of a
single, continuous range of frequencies, or two or more separate,
continuous ranges. The terms "chunk" and "sub-chunk" may also refer to
portions or bands of spectrum.

[0024]"Effecting" an instance of the spectrum assignment process may
comprise one or more of starting/undertaking the process, requesting the
process to be started/undertaken, or indicating the possibility of
starting/undertaking the process.

[0025]The term "mobile communications apparatus", when used herein, may
relate to wireless equipment which is capable of undertaking wireless
communications with one or both of the wireless communications systems.
For example, the term may relate to user equipment (user-portable
wireless equipment), for example a mobile telephone, personal digital
assistant, laptop or PC, to an RFID tag/node or wireless sensor node, or
to a device having WiMAX functionality.

[0026]The term "trigger" may relate to any signal, processing result,
stimulus or circumstance, whether internal or external to the first
wireless communications system, in response to which it is appropriate to
undertake the instance of the spectrum assignment process. In particular,
in respective first to third arrangements, the trigger may be a periodic
basis; a ratio of traffic delivered to traffic offered exceeding a
threshold; or a number of short-term spectrum assignment failures in a
defined period exceeding a threshold (the failures could be consecutive
or non-consecutive). The trigger is based on network conditions and so
the LT spectrum assignment process may be initiated when appropriate.

[0027]In the first arrangement, the method may comprise periodically
effecting instances of the spectrum assignment process, in accordance
with a time period determined in dependence on the network conditions.
The period may be set in dependence on traffic patterns, and the gains
might be achieved from long-term spectrum assignment. In an example, an
operator is located within the business district of a city, and another
operator is located within the surrounding suburbs. During work hours,
people commute to the city centre. In this case, the suburban operator
may shift some of its spectrum resources to the city centre operator. In
the afternoon the opposite transfer may take place, as much of spectrum
is needed in the suburbs (by families, children back from school and
professionals surfing the internet). In this case, a period of a couple
of hours may be a suitable period for LT spectrum assignment. Thus there
may be provided a periodic trigger for the LT spectrum assignment
process. By "periodically" it may be meant that each instance of the
spectrum assignment process is effected following the elapse of a time
interval from the previous instance, the time interval being fixed or
variable. I.e. the spectrum assignment process may be effected repeatedly
from time to time, at particular moments in time.

[0028]In the second arrangement, the method may comprise determining a
traffic delivery success ratio for the first wireless communications
system and effecting the instance of spectrum assignment process in
response to the traffic delivery success ratio being under a
predetermined threshold. The threshold may be set in dependence on the
QoS and the amount of service quality degradation that can be tolerated.
Determining the traffic delivery success ratio may comprise calculating a
ratio of the quantity of traffic delivered to/from the first wireless
communications system to the quantity of traffic which was intended for
delivery to/from the first wireless communications system. Thus there may
be provided a method for triggering the LT spectrum assignment based on
the delivered traffic load status (a network condition).

[0029]In the third arrangement, the spectrum assignment process may be a
long-term spectrum assignment process. The method may comprise receiving
signalling being indicative of the failure of a short-term spectrum
assignment process, and effecting the instance of the long-term spectrum
assignment process in response to the number of failures of the
short-term assignment process exceeding a predetermined threshold. The
threshold may be set in dependence on the grade of service and overall
service quality degradations that the failures may have caused. For
example, if the degradation is severe and the service is a premium
service then there may only be one or two attempts. Thus there may be
provided a method for triggering the LT spectrum assignment based on the
individual status of each ST spectrum assignment process in terms of
failure or success status (i.e. on network conditions). A "long-term"
assignment process may operate on a timescale of approximately a minute
or a couple of minutes, whereas a "short-term" assignment process may
operate on a timescale of approximately a second or a couple of seconds,
for example.

[0030]Effecting the instance of the spectrum assignment process may
comprise obtaining, for each of the wireless communications systems
involved in the process, a preferred spectrum configuration, and
calculating a final spectrum configuration based on the preferred
spectrum configurations. In this way, there may be provided a method for
a democratic and fair LT spectrum assignment process between the involved
wireless communications systems (or their gateways). Each preferred
spectrum configuration may comprise one or more suggested chunks of
spectrum for allocation respectively to one or more of the wireless
communications systems involved in the spectrum assignment process. Thus,
each wireless communications system may estimate the amount of spectrum
it needs, which may involve that system assigning some of its allocated
spectrum to another system or receiving spectrum assigned from another
system, and estimate the amount of spectrum needed by other systems. In a
variant, the information relating to other systems (e.g. the amount of
spectrum needed by that other system, or information allowing the first
wireless communications system to estimate the amount of spectrum needed
by that other system, may be supplied to the first wireless
communications system (or a lead system) (e.g. a RAN or gateway), or any
of the other systems, in advance. The wireless communications system may
also determine a preferred arrangement of each estimated amount of
spectrum, in which arrangement it may be preferred that wireless
communications systems operate within spectrum bands for which they have
a licence to the greatest extent possible. (An operator may attempt to
get the most out of their licence plus more say from an extra shared part
of spectrum. On the other hand, a system which has plenty of spectrum and
say 90% of time under-utilised (e.g. a military or satellite system) may
attempt to rent spectrum resources to other systems as much as possible
to generate more revenue.) One or more of the preferred spectrum
configurations of respective wireless communications systems and the
final spectrum configuration may comprise a region of dedicated bandwidth
and a region of extra shared bandwidth. The region of dedicated bandwidth
may be licensed to one or more operators, while the region of extra
shared bandwidth may comprise parts which are licensed to one or more
operators and/or parts which are unlicensed.

[0031]The term "spectrum configuration" may relate to an arrangement of
one or more portions of spectrum, and may specify one or both of the
amount of spectrum in each portion and/or its position in relation to
other portions of spectrum in the spectrum configuration. For example, by
defining each portion of spectrum with reference to its upper and lower
limits, it is possible to indicate both the size of the portion and its
position in relation to other portions of spectrum. A portion of spectrum
may also be identified by reference to its size and/or a spectrum ID. A
spectrum ID may be a number assigned to each sub-chunk, selected from a
range of possibilities. The arrangement whereby sub-chunks are given
spectrum IDs may be decided before or during the spectrum assignment
process. A spectrum configuration may comprise one or more guard bands,
and one or more regions of licensed/unlicensed spectrum. In addition, the
spectrum configuration may comprise information which associates each
portion of spectrum with a respective entity, which may be a wireless
communications system (e.g. a radio access network) or part thereof, a
cell or base station or a group of cluster thereof, or an uplink or
downlink belonging to any such entity.

[0032]Obtaining the preferred spectrum configurations may comprise
receiving from each of the other said wireless communications systems
signalling to indicate their respective preferred spectrum
configurations, and may further comprise obtaining the preferred spectrum
configuration for the first wireless communications system by

[0033]calculating an amount of additional/surplus spectrum for the first
wireless communications system and using the amount of additional/surplus
spectrum to determine the size of a chunk of spectrum for allocation to
the first wireless communications system;

[0034]estimating the sizes of respective chunks of spectrum for allocation
to each of the other wireless communications systems involved in the
spectrum assignment process; and

[0035]arranging the chunks of spectrum to form the preferred spectrum
configuration for the first wireless communications system.

[0036]Calculating the amount of additional/surplus spectrum for the first
wireless communications system may comprise determining an amount of
spectrum which is required by the first wireless communications system,
or which is available for assignment from the first wireless
communications system to one or more of the other said wireless
communications systems, based on parameters including at least one or
more of a traffic delivery success ratio and a level of interference
associated with the first wireless communications system. The traffic
delivery success ratio may comprise determining a ratio of the quantity
of traffic delivered to/from the first wireless communications system to
the quantity of traffic which was intended for delivery to/from the first
wireless communications system. The level of interference associated with
the first wireless communications system may comprise a current level of
interference, a recent level of interference, a running average of the
level of interference over a predetermined time period or number of
packets or the like, or any other suitable measure of judging the
interference experienced by the first wireless communications system.
Measuring the level of interference may comprise a wireless
communications system which is issuing a portion of spectrum measuring
(or estimating) the signal-to-interference level (SIR) immediately before
and immediately after the borrowing party switches to the assigned
portion of spectrum, which information may be used as described above for
the purposes of a later spectrum assignment. The assigning system may
then compare the SIR values and calculate the difference. It can then say
how much additional interference or SIR loss it has suffered within the
shared band. It is assumed that the capability to measure/estimate
interference or SIR already exists. When measuring interference, the
primary focus is on the borrowed spectrum. For example, the rise or fall
of interference or SIR may be exclusively monitored within parts of the
band currently being shared. A secondary concern is the surrounding band;
it may be of interest how much interference there is from the shared part
of spectrum to the non-shared part.

[0037]The determination may comprise using a mapping table (or look-up
table) to obtain the amount of additional/surplus spectrum from the said
parameters. The method may provide for mapping the traffic delivery
success ratio and the interference level at each wireless communications
system (e.g. at each gateway or RAN) to the requested spectrum level
within the next LT spectrum assignment, for example by employing a
look-up table.

[0038]Calculating the final spectrum configuration may comprise averaging
the preferred spectrum configurations. In one arrangement, the wireless
communications system (e.g. its gateway) currently in charge may consider
all the suggested LT spectrum assignments (preferred spectrum
configurations) to come up with a unique LT spectrum assignment (final
spectrum configuration). For example, to have a fair LT spectrum
assignment, it may average the suggested spectrum chunks over the number
of suggested assignments to come up with the final LT spectrum
assignment.

[0039]Each preferred spectrum configuration may comprise one or more
suggested chunks of spectrum for allocation respectively to one or more
of the wireless communications systems involved in the spectrum
assignment process. The averaging may comprise calculating a final chunk
of spectrum for each of the said wireless communications systems by
summing all of the suggested chunks of spectrum for allocation to that
wireless communications system and dividing by the number of wireless
communications systems involved in the spectrum assignment process.

[0040]The method may be performed by the first wireless communications
system. The first wireless communications system may be a lead wireless
communications system amongst the wireless communications systems
involved in the spectrum assignment process.

[0041]The method may comprise transferring the status of lead wireless
communications system from the first wireless communications system to
another of the plurality of wireless communications systems in dependence
on a predetermined arrangement. The predetermined arrangement may
comprise a round-robin arrangement, or a rotational mechanism to shift
the responsibility for the decision making on the final LT spectrum
assignment from one system (e.g. gateway) to another system (e.g. another
gateway).

[0042]Effecting the instance of the spectrum assignment process may
comprise transmitting to a central spectrum broker module
spectrum-related signalling, and receiving signalling from the central
spectrum broker module to indicate a final spectrum configuration.

[0043]Two or more of the wireless communications systems involved in the
spectrum assignment process comprise two or more respective groups of one
or more network elements, the groups forming parts of the same
overarching network. The method may comprise the said two or more
wireless communications systems independently taking part in the spectrum
assignment process.

[0044]According to a second aspect, there is provided apparatus for
controlling spectrum use in a first wireless communications system which
is operable to take part in a spectrum assignment process involving a
plurality of wireless communications systems including the first wireless
communications system, in which spectrum assignment process one of the
said wireless communications systems assigns a portion of spectrum to at
least one of the other said wireless communications systems, the
apparatus comprising

[0045]spectrum assignment circuitry configured to effect an instance of
the spectrum assignment process in response to a trigger which is based
on network conditions.

[0046]The spectrum assignment circuitry may be configured to effect
instances of the spectrum assignment process periodically, in accordance
with a time period determined in dependence on the network conditions.

[0047]The spectrum assignment circuitry may be configured to determine a
traffic delivery success ratio for the first wireless communications
system and to effect the spectrum assignment process in response to the
traffic delivery success ratio being under a predetermined threshold.

[0048]The spectrum assignment circuitry may be configured to receive
signalling being indicative of the failure of a short-term spectrum
assignment process, and to effect the (long-term) spectrum assignment
process in response to the number of failures of the short-term
assignment process exceeding a predetermined threshold.

[0049]The spectrum assignment circuitry may be configured to obtain, for
each of the wireless communications systems involved in the process, a
preferred spectrum configuration, and to calculate a final spectrum
configuration based on the preferred spectrum configurations.

[0050]The spectrum assignment circuitry may be configured to obtain the
preferred spectrum configurations by receiving from each of the other
said wireless communications systems signalling to indicate their
respective preferred spectrum configurations, and further by obtaining
the preferred spectrum configuration for the first wireless
communications system by calculating an amount of additional/surplus
spectrum for the first wireless communications system and using the
amount of additional/surplus spectrum to determine the size of a chunk of
spectrum for allocation to the first wireless communications system;

[0051]estimating the sizes of respective chunks of spectrum for allocation
to each of the other wireless communications systems involved in the
spectrum assignment process; and

[0052]arranging the chunks of spectrum to form the preferred spectrum
configuration for the first wireless communications system.

[0053]The spectrum assignment circuitry may be configured to calculate the
amount of additional/surplus spectrum for the first wireless
communications system by determining an amount of spectrum which is
required by the first wireless communications system, or which is
available for assignment from the first wireless communications system to
one or more of the other said wireless communications systems, based on
parameters including at least one or more of a traffic delivery success
ratio and a level of interference associated with the first wireless
communications system.

[0054]The spectrum assignment circuitry may be configured to make the
determination by using a mapping table to obtain the amount of
additional/surplus spectrum from the said parameters.

[0055]The spectrum assignment circuitry may be configured to calculate the
final spectrum configuration by averaging the preferred spectrum
configurations.

[0056]Each preferred spectrum configuration may comprise one or more
suggested chunks of spectrum for allocation respectively to one or more
of the wireless communications systems involved in the spectrum
assignment process. The spectrum assignment circuitry may be configured
to average the preferred spectrum configurations by calculating a final
chunk of spectrum for each of the said wireless communications systems by
summing all of the suggested chunks of spectrum for allocation to that
wireless communications system and dividing by the number of wireless
communications systems involved in the spectrum assignment process.

[0057]The spectrum assignment circuitry may be configured to transfer the
status of lead wireless communications system from the first wireless
communications system to another of the plurality of wireless
communications systems in dependence on a predetermined arrangement.

[0058]The spectrum assignment circuitry may be configured to effect the
instance of the spectrum assignment process by transmitting to a central
spectrum broker module spectrum-related signalling, and receiving
signalling from the central spectrum broker module to indicate a final
spectrum configuration.

[0059]The spectrum assignment circuitry may be configured to calculate a
traffic delivery success ratio by determining a ratio of the quantity of
traffic delivered to/from the first wireless communications system to the
quantity of traffic which was intended for delivery to/from the first
wireless communications system.

[0061]According to a third aspect, there is provided a computer program
which, when run on a computer forming part of a network element or an
external controlling element, causes the computer to perform the method
of the first aspect.

[0062]According to a fourth aspect, there is provided a computer program
which, when loaded into a computer forming part of a network element or
an external controlling element, causes the computer to become the
apparatus of the second aspect.

[0063]The computer program of the third or fourth aspect may be carried by
a carrier medium, which may comprise a recording medium and/or a
transmission medium.

[0064]According to a fifth aspect, there is provided a computer program
which, when run on a computer, causes the computer to perform a method of
controlling spectrum use in a first wireless communications system which
is operable to take part in a spectrum assignment process involving a
plurality of wireless communications systems including the first wireless
communications system, in which spectrum assignment process one of the
said wireless communications systems assigns a portion of spectrum to at
least one of the other said wireless communications systems, the method
comprising

[0065]effecting an instance of the spectrum assignment process in response
to a trigger which is based on network conditions.

[0066]According to a sixth aspect, there is provided a computer program
for controlling spectrum use in a first wireless communications system
which is operable to take part in a spectrum assignment process involving
a plurality of wireless communications systems including the first
wireless communications system, in which spectrum assignment process one
of the said wireless communications systems assigns a portion of spectrum
to at least one of the other said wireless communications systems, the
computer program comprising

[0067]spectrum assignment code configured to effect an instance of the
spectrum assignment process in response to a trigger which is based on
network conditions.

[0068]Any circuitry may include one or more processors, memories and bus
lines. One or more of the circuitries described may share circuitry
elements.

[0069]The present invention includes one or more aspects, embodiments or
features in isolation or in various combinations whether or not
specifically stated (including claimed) in that combination or in
isolation.

[0070]The above summary is intended to be merely exemplary and
non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0071]A description is now given, by way of example only, with reference
to the accompanying drawings, in which:

[0083]FIG. 11 illustrates a second arrangement including triggering the LT
spectrum assignment based on the delivered traffic load status;

[0084]FIG. 12 illustrates a scenario in which a base station from a
radio-access network has failed to earn the spectrum it has requested
before the start of spectrum negotiations with another base station;

[0085]FIG. 13 illustrates a third arrangement including triggering the LT
spectrum assignment based on the individual status of each ST spectrum
assignment process in terms of failure or success status;

[0086]FIG. 14 shows a number of preferred spectrum configurations
suggested by the gateways of different wireless communications systems;

[0087]FIG. 15 illustrates a process of combining different preferred
spectrum configurations to establish a final spectrum configuration of
the LT spectrum assignment process;

[0089]FIG. 17 illustrates the impact of the invention on the stages of
spectrum assignment.

DETAILED DESCRIPTION

[0090]Embodiments of the invention relate to methods for long-term (LT)
spectrum assignments between multiple RANs, and various triggers for
starting the LT spectrum assignments are disclosed.

[0091]FIG. 9 relates to a first trigger type involving periodic activation
of long-term spectrum assignment processes, wherein multiple, parallel ST
spectrum allocations are performed and long-term spectrum assignment is
called on a regular and periodic basis, in accordance with a time period
determined in dependence on the network conditions.

[0092]FIGS. 10 and 11 relate to a second trigger type involving triggering
the LT spectrum assignment based on the delivered traffic load status
(i.e. taking into account the impact of delivered traffic load). In this
case, there is no primary RAN, and no priority between RANs. FIG. 10
shows a scenario in which multiple short term spectrum assignment are
occurring simultaneously in different networks and being monitored by the
gateways of each network. The arrows in FIG. 10 illustrate signalling
being passed between the various elements of the network.

[0093]Each gateway GW1-3 is responsible for a number of ST spectrum
assignments in its own RAN1-3. The gateway GW1-3 after every couple of ST
spectrum assignment processes requires the ratio of delivered traffic to
the traffic supposed to be delivered for the previous ST spectrum
assignments, as shown in FIG. 11. If the ratio is below a specific
threshold, the gateway GW1-3 sends a request for LT spectrum assignment
to the other gateways GW1-3. If the gateway GW1-3 with the problem, which
sends the request, is a primary gateway, its request must be accepted.
Otherwise, the other gateways GW consider their own traffic delivery
success ratio, and if it is also below or equal to a specific threshold,
they agree for a LT spectrum assignment, as shown in FIG. 11.

[0094]FIGS. 12 and 13 relate to a third trigger type involving triggering
the LT spectrum assignment based on the individual status of each ST
spectrum assignment process in terms of failure or success status
(request from ST spectrum assignment).

[0095]It is assumed that multiple short-term spectrum assignments are
ongoing. As an example, FIG. 12 shows a scenario in which base station
BS5 of RAN2 has failed to obtain a requested chunk of spectrum from base
station BS1 of RAN1.

[0096]If multiple failures of the ST spectrum assignment process are
detected by any of the gateways (i.e. the number of failed attempts from
the base stations is above a threshold), the gateway will send a request
for LT spectrum assignment, as shown in FIG. 13.

[0097]A LT spectrum assignment process may be undertaken in response to
any of the triggers.

[0098]In step 1, after approval and start of the LT spectrum assignment
process, all the involved gateways first on a simultaneous basis evaluate
their total traffic delivery success ratio since the last LT spectrum
assignment process.

[0099]In step 2, the gateways evaluate the current level of interference
inflicted on all the base stations which they control.

[0100]In step 3, the gateways map the traffic delivery success ratios and
current level of interference to the total extra spectrum they require or
the spectrum they want to release by employing a lookup table. The higher
the traffic deliver success ratio and the lower the interference, the
lower the desire to change the current spectrum configuration.

[0101]In step 4, one gateway becomes the master gateway and the decision
maker. (The responsibility of being master gateway is changed on a
periodic basis. In the next LT spectrum assignment process, the current
master gateway will be replaced with another one, in a round-robin
fashion.)

[0102]In step 5, each gateway sends a preferred spectrum configuration
(its new spectrum arrangement which it has in mind) to the gateway in
charge. For example, FIG. 14 shows the preferred spectrum configurations
(suggested spectrum arrangements) of the three gateways GW1-3. Each
preferred spectrum configuration consists of suggested chunks of spectrum
for allocation respectively to the RANs involved in the LT spectrum
assignment process.

[0103]In step 5, the gateway currently in charge considers all the
preferred spectrum configurations to come up with a final spectrum
configuration to form the basis of the LT spectrum assignment. To have a
fair LT spectrum assignment, in one arrangement, the gateway may average
the suggested spectrum chunks over the number of preferred spectrum
configurations to come up with the final spectrum configuration. In an
example of another arrangement, as shown in FIG. 15, two different
spectrum sizes are suggested for allocation to RAN3 by gateway GW2 and
gateway GW3. In this example, gateway GW1 indicates that it is happy with
the current spectrum configuration (or that it is happy with its
suggested chunk in previous LT assignments) by not putting forward a new
suggestion. These two chunks are added together and divided by three to
come up with the amount of spectrum to be allocated to RAN3. In any case,
the position of the chunks within a spectrum configuration is set
according to a predefined arrangement (for example kept within a data
policy as part of the spectrum policies in the central database). For
example, one operator may always take the first chunk by a formal
agreement (regardless of the amount of spectrum), a second operator may
take the second chunk and a third operator may take a final chunk. The
final spectrum configuration will be valid for upcoming ST spectrum
assignment processes until the next LT spectrum assignment process is
triggered.

[0104]After completion of the long-term spectrum assignment process, each
RAN would register the decision in its own spectrum manager, for
accounting purposes. The spectrum manager includes spectrum policies used
for further accounting activities.

[0106]In a variant to the round-robin-fashion transfer of the status of
master gateway described above, a centralised long-term spectrum
assignment brokering system is used with all the gateways actively
sending their situation parameters and requests for extra spectrum to the
brokering system. In order to make a decision, the central spectrum
broker needs all the information from all the gateways, and so signalling
is transmitted from the gateways to the core network and the central
spectrum broker every couple of minutes. As the LT spectrum assignment
process and brokering might happen on a couple of minutes basis, avoiding
a central brokering system as proposed by the round-robin approach may
provide a faster time frame for LT spectrum assignment, avoiding the
further delays due to a fully-centralised process. Currently each gateway
and its unique spectrum manager is located in each RAN. The central
spectrum broker may be located inside the core network.

[0107]The above disclosure can be applied to a RAN with multiple gateways
where each geographic area of the RAN has a gateway assigned to it and
might get engaged in negotiations with other RANs according to its own
specific spectrum demands and based on the protocols described above.

[0108]It will be appreciated that the aforementioned circuitry may have
other functions in addition to the mentioned functions, and that these
functions may be performed by the same circuit.

[0109]The applicant hereby discloses in isolation each individual feature
described herein and any combination of two or more such features, to the
extent that such features or combinations are capable of being carried
out based on the present specification as a whole in the light of the
common general knowledge of a person skilled in the art, irrespective of
whether such features or combinations of features solve any problems
disclosed herein, and without limitation to the scope of the claims. The
applicant indicates that aspects of the present invention may consist of
any such individual feature or combination of features. In view of the
foregoing description it will be evident to a person skilled in the art
that various modifications may be made within the scope of the invention.

[0110]The invention may extend to the following statements:
[0111]Statement 1. A method of controlling spectrum use in a first
wireless communications system which is operable to take part in a
spectrum assignment process involving a plurality of wireless
communications systems including the first wireless communications
system, in which spectrum assignment process one of the said wireless
communications systems assigns a portion of spectrum to at least one of
the other said wireless communications systems, the method comprising

[0112]effecting an instance of the spectrum assignment process in response
to a trigger which is based on network conditions. [0113]Statement 2. The
method of statement 1 comprising periodically effecting instances of the
spectrum assignment process, in accordance with a time period determined
in dependence on the network conditions. [0114]Statement 3. The method of
statement 1 or 2 comprising determining a traffic delivery success ratio
for the first wireless communications system and effecting the instance
of spectrum assignment process in response to the traffic delivery
success ratio being under a predetermined threshold. [0115]Statement 4.
The method of any preceding statement wherein the spectrum assignment
process is a long-term spectrum assignment process, the method comprising
receiving signalling being indicative of the failure of a short-term
spectrum assignment process, and effecting the instance of the long-term
spectrum assignment process in response to the number of failures of the
short-term assignment process exceeding a predetermined threshold.
[0116]Statement 5. The method of any preceding statement wherein
effecting the instance of the spectrum assignment process comprises
obtaining, for each of the wireless communications systems involved in
the process, a preferred spectrum configuration, and calculating a final
spectrum configuration based on the preferred spectrum configurations.

[0117]Statement 6. The method of statement 5 wherein obtaining the
preferred spectrum configurations comprises receiving from each of the
other said wireless communications systems signalling to indicate their
respective preferred spectrum configurations, and further comprises
obtaining the preferred spectrum configuration for the first wireless
communications system by

[0118]calculating an amount of additional/surplus spectrum for the first
wireless communications system and using the amount of additional/surplus
spectrum to determine the size of a chunk of spectrum for allocation to
the first wireless communications system;

[0119]estimating the sizes of respective chunks of spectrum for allocation
to each of the other wireless communications systems involved in the
spectrum assignment process; and

[0120]arranging the chunks of spectrum to form the preferred spectrum
configuration for the first wireless communications system.
[0121]Statement 7. The method of statement 6 wherein calculating the
amount of additional/surplus spectrum for the first wireless
communications system comprises determining an amount of spectrum which
is required by the first wireless communications system, or which is
available for assignment from the first wireless communications system to
one or more of the other said wireless communications systems, based on
parameters including at least one or more of a traffic delivery success
ratio and a level of interference associated with the first wireless
communications system. [0122]Statement 8. The method of statement 7
wherein the determination comprises using a mapping table to obtain the
amount of additional/surplus spectrum from the said parameters.
[0123]Statement 9. The method of any of statements 5 to 8 wherein
calculating the final spectrum configuration comprises averaging the
preferred spectrum configurations. [0124]Statement 10. The method of
statement 9 wherein each preferred spectrum configuration comprises one
or more suggested chunks of spectrum for allocation respectively to one
or more of the wireless communications systems involved in the spectrum
assignment process, and wherein the averaging comprises calculating a
final chunk of spectrum for each of the said wireless communications
systems by summing all of the suggested chunks of spectrum for allocation
to that wireless communications system and dividing by the number of
wireless communications systems involved in the spectrum assignment
process. [0125]Statement 11. The method of any of statements 5 to 10
performed by the first wireless communications system, wherein the first
wireless communications system is a lead wireless communications system
amongst the wireless communications systems involved in the spectrum
assignment process. [0126]Statement 12. The method of statement 11
comprising transferring the status of lead wireless communications system
from the first wireless communications system to another of the plurality
of wireless communications systems in dependence on a predetermined
arrangement. [0127]Statement 13. The method of any of statements 1 to 4
wherein effecting the instance of the spectrum assignment process
comprises transmitting to a central spectrum broker module
spectrum-related signalling, and receiving signalling from the central
spectrum broker module to indicate a final spectrum configuration.
[0128]Statement 14. The method of statement 3 or 7 wherein calculating a
traffic delivery success ratio comprises determining a ratio of the
quantity of traffic delivered to/from the first wireless communications
system to the quantity of traffic which was intended for delivery to/from
the first wireless communications system. [0129]Statement 15. The method
of any preceding statement wherein the spectrum assignment process is a
long-term spectrum assignment process forming part of a larger spectrum
sharing scheme further including at least a short-term spectrum
assignment process. [0130]Statement 16. The method of any preceding
statement wherein the spectrum assignment process involves at least three
wireless communications systems including the first wireless
communications system. [0131]Statement 17. The method of any of
statements 5 to 16 wherein one or more of the preferred spectrum
configurations of respective wireless communications systems and the
final spectrum configuration comprises a region of dedicated bandwidth
and a region of extra shared bandwidth. [0132]Statement 18. The method of
any preceding statement wherein two or more of the wireless
communications systems involved in the spectrum assignment process
comprise two or more respective groups of one or more network elements,
the groups forming parts of the same overarching network, the method
comprising the said two or more wireless communications systems
independently taking part in the spectrum assignment process.
[0133]Statement 19. Apparatus for controlling spectrum use in a first
wireless communications system which is operable to take part in a
spectrum assignment process involving a plurality of wireless
communications systems including the first wireless communications
system, in which spectrum assignment process one of the said wireless
communications systems assigns a portion of spectrum to at least one of
the other said wireless communications systems, the apparatus comprising

[0134]spectrum assignment circuitry configured to effect an instance of
the spectrum assignment process in response to a trigger which is based
on network conditions. [0135]Statement 20. The apparatus of statement 19
wherein the spectrum assignment circuitry is configured to effect
instances of the spectrum assignment process periodically, in accordance
with a time period determined in dependence on the network conditions.
[0136]Statement 21. The apparatus of statement 19 or 20 wherein the
spectrum assignment circuitry is configured to determine a traffic
delivery success ratio for the first wireless communications system and
to effect the spectrum assignment process in response to the traffic
delivery success ratio being under a predetermined threshold.
[0137]Statement 22. The apparatus of any of statements 19 to 21 wherein
the spectrum assignment process is a long-term spectrum assignment
process, and wherein the spectrum assignment circuitry is configured to
receive signalling being indicative of the failure of a short-term
spectrum assignment process, and to effect the long-term spectrum
assignment process in response to the number of failures of the
short-term assignment process exceeding a predetermined threshold.
[0138]Statement 23. The apparatus of any of statements 19 to 22 wherein
the spectrum assignment circuitry is configured to obtain, for each of
the wireless communications systems involved in the process, a preferred
spectrum configuration, and to calculate a final spectrum configuration
based on the preferred spectrum configurations. [0139]Statement 24. The
apparatus of statement 23 wherein the spectrum assignment circuitry is
configured to obtain the preferred spectrum configurations by receiving
from each of the other said wireless communications systems signalling to
indicate their respective preferred spectrum configurations, and further
by obtaining the preferred spectrum configuration for the first wireless
communications system by

[0140]calculating an amount of additional/surplus spectrum for the first
wireless communications system and using the amount of additional/surplus
spectrum to determine the size of a chunk of spectrum for allocation to
the first wireless communications system;

[0141]estimating the sizes of respective chunks of spectrum for allocation
to each of the other wireless communications systems involved in the
spectrum assignment process; and

[0142]arranging the chunks of spectrum to form the preferred spectrum
configuration for the first wireless communications system.
[0143]Statement 25. The apparatus of statement 24 wherein the spectrum
assignment circuitry is configured to calculate the amount of
additional/surplus spectrum for the first wireless communications system
by determining an amount of spectrum which is required by the first
wireless communications system, or which is available for assignment from
the first wireless communications system to one or more of the other said
wireless communications systems, based on parameters including at least
one or more of a traffic delivery success ratio and a level of
interference associated with the first wireless communications system.
[0144]Statement 26. The apparatus of statement 25 wherein the spectrum
assignment circuitry is configured to make the determination by using a
mapping table to obtain the amount of additional/surplus spectrum from
the said parameters. [0145]Statement 27. The apparatus of any of
statements 23 to 26 wherein the spectrum assignment circuitry is
configured to calculate the final spectrum configuration by averaging the
preferred spectrum configurations. [0146]Statement 28. The apparatus of
statement 27 wherein each preferred spectrum configuration comprises one
or more suggested chunks of spectrum for allocation respectively to one
or more of the wireless communications systems involved in the spectrum
assignment process, and wherein the spectrum assignment circuitry is
configured to average the preferred spectrum configurations by
calculating a final chunk of spectrum for each of the said wireless
communications systems by summing all of the suggested chunks of spectrum
for allocation to that wireless communications system and dividing by the
number of wireless communications systems involved in the spectrum
assignment process. [0147]Statement 29. The apparatus of any of
statements 23 to 28 wherein the first wireless communications system is a
lead wireless communications system amongst the wireless communications
systems involved in the spectrum assignment process. [0148]Statement 30.
The apparatus of statement 29 wherein the spectrum assignment circuitry
is configured to transfer the status of lead wireless communications
system from the first wireless communications system to another of the
plurality of wireless communications systems in dependence on a
predetermined arrangement. [0149]Statement 31. The apparatus of statement
23 wherein the spectrum assignment circuitry is configured to effect the
instance of the spectrum assignment process by transmitting to a central
spectrum broker module spectrum-related signalling, and receiving
signalling from the central spectrum broker module to indicate a final
spectrum configuration. [0150]Statement 32. The apparatus of statement 21
or 25 wherein the spectrum assignment circuitry is configured to
calculate a traffic delivery success ratio by determining a ratio of the
quantity of traffic delivered to/from the first wireless communications
system to the quantity of traffic which was intended for delivery to/from
the first wireless communications system. [0151]Statement 33. The
apparatus of any of statements 19 to 32 wherein the spectrum assignment
process is a long-term spectrum assignment process forming part of a
larger spectrum sharing scheme further including at least a short-term
spectrum assignment process. [0152]Statement 34. The apparatus of any of
statements 19 to 33 wherein the spectrum assignment process involves at
least three wireless communications systems including the first wireless
communications system. [0153]Statement 35. The apparatus of any of
statements 23 to 34 wherein one or more of the preferred spectrum
configurations of respective wireless communications systems and the
final spectrum configuration comprises a region of dedicated bandwidth
and a region of extra shared bandwidth. [0154]Statement 36. The apparatus
of any of statements 19 to 35 wherein two or more of the wireless
communications systems involved in the spectrum assignment process
comprise two or more respective groups of one or more network elements,
the groups forming parts of the same overarching network, the two or more
wireless communications systems independently taking part in the spectrum
assignment process. [0155]Statement 37. A computer program which, when
run on a computer forming part of a network element or an external
controlling element, causes the computer to perform the method as in any
of statements 1 to 18. [0156]Statement 38. A computer program which, when
loaded into a computer forming part of a network element or an external
controlling element, causes the computer to become the apparatus as in
any of statements 19 to 36. [0157]Statement 39. A computer program as in
any of statements 37 to 38, carried by a carrier medium. [0158]Statement
40. The computer program of statement 39, wherein the carrier medium is a
recording medium. [0159]Statement 41. The computer program of statement
39, wherein the carrier medium is a transmission medium.